Piano World Home Page Forums Our Most Popular Forums Piano Tuner-Technicians Forum Question about possibility of lightening up a dp action

Blow distance is a distance between lowest and highest hammer position, I'd like you to measure it at the point I showed

Strikeweight is weight of hammer whet hammer is supported at it's pivot point, in your piano you can measure strikeweight when hammer is in the piano because hammer pivot bearing in digital pianos have almost zero friction so it won't interfere with meausrements. It is important also that hammer shank is horizontal when measuring and that hammer is resting on scale at exact point I showed, you will probably need to use something inbetween hammer and scale like this black triangle on my very beautiful drawing. Usually you need a scale that is capable of measuring to 0.1g precision but for this 1g might be sufficient because this hammer will weight much more than real piano hammer.
There is more about measuring strikeweight in acoustic pianos: http://www.stanwoodpiano.com/NTM.pdf

I approximately measured from pictures hammer blow distance of 28mm and action ratio of 2.6:1 then I calculated back strike weight of 27g from this and your measurements of 60 and 52g of DW and UW and assumption that there is none counterweights in the middle notes of this keyboard. How close I am?

Ok, I understand it, and I do happen to have a little scale that measures to 0.1g precision. (and i must have a free coat hanger hanging around somewhere in my closet, does it have to be a black one or will a different color work as well?)

I don't know if it's too great to put the scale between the key and the hammer, as I think the hammer won't be exactly horizontal that way. But if I understand this correctly I can just take out one of the hammers (around middle c I guess) and hang it from it's pivot point and then weigh it at the point you have drawed (admittedly very beautifully), right?

I think I can do it tomorrow. We'll see how close your are!

Well, I don't know how close is close in piano measurements, but I'd say you were pretty close actually!

(there are no counterweights in the mid-section, only in the bass section)



For the black key hammers (which are 2mm higher than the white key hammers in rest position), you were spot on with the hammer blow distance: 28mm, and so it is 30mm for the white key hammers.



Looking at the hammers something else came to mind, it's not something I would really like to do, but I wonder if ratio-wise it would make a noticable difference.



I wonder if as I would drill 1 or 2 of those small holes in the hammers a bit bigger, if that would take away enough material (on both sides of the hammer) to make a noticable difference?

That's a bit harder to reverse if the effect is undesired!?

Indeed.

Well I guess i could put small screws in there to add some weight again or something if I would want to reverse it, but yeah it isn't quite as reversible as the idea with springs. But on the other hand if it would have a big effect (say 10-15g less downweight) it would be a simpler solution. But I can't image it would have that kind of effect, since the material that would be removed this way looks to be pretty minimal.

It's an idea, but I wouldn't really like to do this, for the reversability reason and also maybe something could go wrong and the metal could get loose or something like that.

Get some 10 or 12 gram lead piano key weights.
Temporarily stick a few to the tops of the keys, on the plastic playing surfaces, above the places in the wood where you could drill through and insert the weights.
Test as best you can, to be sure it improves the touch.
If good, drill through the keys from the side, using a forstner bit, which will make a clean hole.
The keys are short, the moment of inertia won't be that great.
Place the key on its side on an anvil (a small bench vise will do) and tap the weight with a large phillips screwdriver, just enough to tighten the weight, or use glue if you prefer.

Thanks! I will consider this option. Would it be best to drill through the keys entirely or just enough for the lead weights to fit in?

What's special about a philips screwdriver?

It was close, but not close enough haha

I use a coefficient which could be called "inertial heaviness coefficient":

(strikeweight) x (blow distance)^2

it is proportional to the time of keystroke given torque exerted on key, lower values gives lighter and faster action, higher gives heavier and slower. It can be used to exchange hammer mass for blow distance. It is independent of the action leverage/key dip, (hence the torque, not the force exerted at the end of the key), I treat leverage/keydip as separate thing

For this kawai it will equals 23,8g*30mm^2 = 21420
equivalent acoustic will be 10,6g*45mm^2 = 21262
so 10,6g strikeweight for middle C and this is medium-high "heavines" but estimating inertia from strikeweight is approximate because it depends on mass distribution between hammer head and hammer shank and in this case there is probably proportionally more mass in hammer shank than in real piano hammer, so inertia will be slightly lower than and I will say that this action has exactly medium inertia compared to typical acoustics.

But I see something else there, black keys have shorter blow distance and it looks like black key hammers are lighter also, as if they intentionally designed the black keys to be lighter, does it feel like that? Can you measure strikeweight of black key hammer adjacent to the white key you measured?

Thanks for the explanation, I got most of it on second read.


Yes, sure I can.

Is there more that I should measure other than that? Because I use the piano in the meantime so everytime I have to disconnect everything and open it up etc. I was hoping this was the last time I had to do that before actually starting to do something about the touchweight, haha.

I don't feel like the black keys are lighter, but I haven't measured it yet either. I have never heard anyone say something about black keys feeling lighter on a wooden kawai action so I don't think that's the case. But maybe your right, the hammers could be lighter for whatever reason, as they obviously have a slightly different resting position as well.

It might that they were trying to compensate something else with that, maybe those short keys, maybe there is different keydip on blacks, in the end only thing that matters is if it feels the same like white keys, but if you will proceed with that idea of driling those holes in hammers, we'd better know what is going on with those black keys.

and from all the information you've gathered so far, I would reduce the weight of these hammers by 3-4g

Hmm.. agreed, best to know what's up with that. (+1 for the spring idea?)


You mean reducing the hammer weight by 3-4 gram would result in 10-15 gram reduction in downweight?

Even then, I don't know If reducing the hammer weight precisely like that is really doable, if that's what you mean.

Actually with your idea of drilling those existing holes it would be very precise

Hmmm. Interesting.

Do you think that could actually take off 3-4 gram?

I need to know exact thickness of those metal parts and diameter of those existing holes, then I can calculate how large hole you need to drill there

That's great, you sure know how to calculate things.

I will measure everything tomorrow!

I still like reducing the weight of the hammers much better than adding weights to the keys...

Probably way easier than installing and calibrating springs - reversible by filling with copper wire or even solder (not hot) pieces.

Ron Koval

Good to take into consideration, didn't think of that yet!

Taking off 4g from those hammers will lower downweight to reasonable range AND inertia to low-mid level, it will make considerable difference.

There is one more thing you can do to make this action less slugish, put some more felt under the backs of keys to lower their fronts, this will reduce key dip and hammer blow distance making this action even faster (the same effect as left pedal on upright but of course to a lesser extent). Of course if you don't like slightly shallower key dip don't do it, but it's always a possibility. It will also compensate one side effect of reducing hammer weight, which is higher final hammer velocity which will produce higher midi velocities (some recalibration of your velocity curves will be needed for sure).
I would suggest putting 1-2mm thick felt in there which will reduce keydip by 0.7-1.5mm and hammer blow distance by 2-4mm

All very, very useful information, I'm learning alot here! think this will go from a controller I like alot to a controller I love.

I don't think I understand the higher final hammer velocity, how does that work exactly? Is it because a lighter hammer will swing easier, or something like that?